Needle stop apparatus for sewing machine

ABSTRACT

A needle stop apparatus for use in a motor-driven sewing machine, in which the needle of the sewing machine is automatically stopped at a predetermined position by turning off a controlled rectifier connected in series with the motor, said turn off of the controlled rectifier being effected by shortcircuiting a gate trigger signal generator upon detecting that the needle is coming to the predetermined position when the motor is prepared to be stopped, and any manual movement of the needle does not cause the motor to start after a predetermined time interval has elapsed from the motor stop, and further it is possible to operate the sewing machine in a one-stitch mode.

United States Patent NEEDLE STOP APPARATUS FOR SEWING MACHINE lnventors Appl. No. Filed Patented Assignee Priorities 4 Claims, 7 Drawing Figs. US. Cl 318/468, 1 12/219, 318/470, 318/675 Int. Cl H02p 3/08, GOSd 3/00 Field of Search 318/266,

Primary Examiner-Thomas .l. Kozma Assistant Examiner-H. Huberfeld Attorney-Stevens, Davis, Miller and Mosher ABSTRACT: A needle stop apparatus for use in a motordriven sewing machine, in which the needle of the sewing machine is automatically stopped at a predetermined position by turning off a controlled rectifier connected in series with the motor, said turn off of the controlled rectifier being effected by short-circuiting a gate trigger signal generator upon detecting that the needle is coming to the predetermined position when the motor is prepared to be stopped, and any manual movement of the needle does not cause the motor to start after a predetermined time interval has elapsed from the motor stop, and further it is possible to operate the sewing machine in a one-stitch mode.

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PATENTEBNUV 23 new 3.622.854

sum 2 0F 3 PATENTEUuuv 23 Ian 3, 22 54 sum 3 or 3 NEEDLE STOP APPARATUS FOR SEWING MACHINE The present invention relates to a needle stop apparatus for a sewing machine.

In stopping a motor-driven sewing machine, considerable skill is required to stop the needle in a desired position without resorting to any special device. In using a motor-driven sewing machine, when the sewing machine is to be stopped, it has been customary to stop the motor at first and then slowly operate the sewing machine manually to bring the needle to a desired position whenever the position of the needle deviates from the desired position upon stoppage of the motor.

Because of this practice, the conventional motor-driven sewing machine has the drawback that the operation is cumbersome and the operation efficiency low although the sewing machine is driven by a motor. Furthermore, with the conventional motor-driven sewing machine it is difficult to operate the machine slowly one stitch after another.

The present invention aims to obviate such drawback of the conventional motor-driven sewing machine.

The needle stop apparatus according to the present invention comprises an electric motor for driving a needle, a solid state controlled rectifier element connected in series with said electric motor which in turn is connected to an AC power source, a gate trigger signal generator including a signal level adjusting a variable resistor element, means for connecting the slider of said variable resistor element with the gate terminal of said solid state controlled element, a switch operatively associated with the slider of said variable resistor element so as to be closed when said signal level is lowest, a variable impedance element connected in parallel to a portion of said gate trigger signal generator through said switch and means for changing the impedance of said variable impedance element upon detecting the position of said needle.

An object of the present invention is to stop the needle positively in a desired position by detecting the position of the needle at the time of stopping the sewing machine and interrupting the current passing through the solid state controlled rectifier element in series connection with the electric motor when said needle is located in the desired position, and thereby to enhance the sewing operation efiiciency.

Another object of the invention is to ensure that the electric motor will not be restarted when the needle is moved manually upon passage of a certain time after the needle has been brought to a halt, and thereby to enhance the safety of the sewing machine.

Still another object of the invention is to make it possible to operate the needle slowly one stitch after another.

Still another object of the invention is to stop the needle in an optionally selected position by switching a control switch.

A further object of the invention is to construct the sewing machine such that when the electric motor has been locked due to penetration of the cloth being sewn into the sewing machine or for other reasons, with the needle being in a position other than the present stop position, the current supply to the electric motor is automatically interrupted upon passage of a certain time, irrespective of the position of the needle, thereby enhancing the safety of the sewing machine.

These and other objects, features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings which show embodiments of the invention and in which:

FIG. I is a circuit diagram showing one embodiment of the needle stop apparatus for a sewing machine according to the present invention;

FIG. 2 is a front elevation of a sewing machine incorporating the needle stop apparatus shown in FIG. 1;

FIG. 3 is a fragmentary side elevation looking in the direction of the arrows III-III of FIG. 2;

FIG. 4 is a circuit diagram showing another embodiment of the needle stop apparatus of the invention.

FIG. 5 is a front elevation of a sewing machine incorporating the needle stop apparatus shown in FIG. 4;

FIG. 6 is a fragmentary side elevation looking in the direction of the arrows VIVI ofFIG. 5; and

FIG. 7 is a circuit diagram showing still another embodiment of the needle stop apparatus of this invention.

Referring first to FIGS. 1 to 3, reference numerals I, 2 designate AC source lines. Between the AC source lines I and 2 are connected in series an SCR 3, and the field winding 4 and the armature 5 of an associated series commutator motor. Also connected between the AC source lines I and 2 is a gate trigger signal generator 11 consisting of a series circuit of a resistor 6, a variable resistor 8 having a slider 7, a resistor 9 and a diode 10. The diode I0 is connected to the AC source line 2 on the cathode side. The slider 7 and the gate terminal I2 of the SCR 3 are connected with each other through a diode 13. The diode I3 is connected in such a position that the cathode thereof faces the gate terminal 12. Further, a resistor I5 is connected between the gate terminal 12 and the cathode terminal 14 to protect the gate of the SCR 3.

A diode 16 has its positive electrode connected to the junction of the resistors 8 and 9 of the gate trigger signal generator 11, with the negative electrode connected to one terminal of a switch 17. The other terminal of the switch 17 is connected to the collector of a transistor 18 which has its emitter connected to the AC source line 2. A diode I6 is provided for the purpose of preventing inverse voltage breakage of the transistor 18 and is unnecessary when the resistance to inversewoltage of the transistor is large.

The operation of the switch 17 is associated with the vertical movement of the slider 7 of the variable resistor 8, in such a manner that the switch 17 is closed only when the slider 7 is at the lowest end of its stroke and is opened when the slider 7 moves upward even slightly.

A resistor 19 is connected at one terminal to the base of the transistor l8, and one terminal of another resistor 20 and the collector of a transistor 21 are connected to the other terminal of said resistor 19. The other terminal of the resistor 20 has the negative electrode of a diode 22 and one terminal of a capacitor 23 connected thereto. The positive electrode of the diode 22 is connected to the AC source line I and the other terminal of the capacitor 23 is connected to the AC source line 2.

The base of the transistor 21 has one terminal of a reed switch 24 and one terminal of a resistor 25 connected thereto. The other terminal of the reed switch 24 is connected to the AC source line 2. To the other terminal of the resistor 25 are connected one terminal of another resistor 26 and one terminal of a capacitor 27. The other terminal of the resistor 26 is connected to the negative electrode of a diode 28 which in turn is connected to the cathode terminal 14 of the SCR 3 at the positive electrode. The other terminal of the capacitor 27 is connected to the AC source line 2.

The reed switch 24 is mounted in a stationary position on the head of an associated sewing machine as shown in FIG. 2. A magnet 30, mounted on the flywheel 31 of the sewing machine, operates in conjunction with the vertical movement of a needle. Its location is such that it is opposed by the reed switch 24 only when the needle is in its upper position.

An electric motor is housed in the body of the sewing machine, with the drive shaft thereof operatively connected through a belt or gears with an operating shaft 32 of the sewing machine on which the flywheel 31 is mounted.

FIG. 3 shows the relative position of the magnet 30 and the reed switch 24, as viewed in the direction of the arrows III-III of FIG. 2, when the needle is in its upper position and the reed switch 24 is opposed by the magnet 30.

When the AC source lines 1 and 2 are impressed with voltage, the capacitor 23 is constantly charged through the diode 22. Therefore, the capacitor 23 can be regarded as a sort of battery.

If a bias voltage is not impressed on the transistor 2! when the slider 7 is at the lowest end of its stroke and the switch 17 is closed, a bias voltage is impressed across the base and emitter of the transistor 18 from the capacitor 23 through the resistors 20.and 19, to keep said transistor 18 energized.

Therefore, the slider 7 and the AC source line 2 are electrically shorted through the transistor 18 and a trigger voltage is not impressed on the gate of the SCR 3. Consequently, the SCR 3 is held in the deenergized state and hence the motor is held inoperative.

When the slider 7 is slightly moved upward to open the switch 7 operatively associated therewith, the impedance between the slider 7 and the AC source line 2 is dissociated from the transistor 18. Therefore, when the AC source line 1 is charged with positive voltage, a current which varies in the form of a sine wave flows from the AC source line 1 to 2 through the resistor 6, the variable resistor 8, the resistor 9 and the diode 10. As a result, a voltage in proportion to the aforesaid current, that is, a voltage corresponding to the positive half wave of the AC source voltage, develops across the slider 7 and the AC source line 2. The SCR 3 is energized at the phase wherein the voltage reaches a value large enough to trigger the gate of said SCR, and thus the motor is set in operation. The voltage developed across the slider 7 and the AC source line 2 becomes larger as the slider 7 is moved upward and accordingly the angle of energization of the SCR 3 becomes larger and the speed ofthe motor increases.

On the other hand, when the AC source line 1 is charged with negative voltage, that is, the voltage corresponding to the negative half wave of the source voltage, a reverse voltage is impressed on the SCR 3, so that the SCR 3 blocks the current being supplied to the motor. However, the motor continues to rotate under mechanical inertia until the next positive half cycle comes.

Now, when the slider 7 is moved downward to the lowest end of its stroke to stop the motor, the switch 17 is closed and the transistor 18 is again connected between the slider 7 and the AC source line 2. In this case, however, if the transistor 18 is in the energized state, the slider 7 and the AC source line 2 will be electrically shorted with each other and the SCR 3 will not be energized thereafter, whereas if the transistor 18 is in the deenergized state, no change will be caused by the transistor 18 between the slider 7 and the AC source line 2, and the SCR 3 will be energized at every half cycle, even after the switch 17 is closed, and the motor will continue to rotate at a predetermined low speed.

Namely, whether the motor is stopped or not after closure of the switch 17 is determined by whether the transistor 18 is in the energized state or in the deenergized state. Whether the transistor 18 is in the energized state or in the deenergized state is determined by whether the transistor 21 is in the deenergized state or in the energized state.

Once the SCR 3 has been energized, the capacitor 27 is charged through the diode 28 and the resistor 26, and the voltage thus charged serves as a bias source for the transistor 21. It will, therefore, be understood that whether the transistor 21 is in the deenergized state or in the energized state is determined by whether the reed switch 24 is closed or opened.

As stated, the reed switch 24 is mounted on the stationary portion of the head 29 of the sewing machine and the magnet 30 is mounted on the flywheel 31 mounted on the operating shaft 32 of the machine for rotation therewith, as shown in H6. 2. Therefore, when the needle is located in its upper position upon closure of the switch 17, and the reed switch 24 and the magnet 30 are opposed by each other and the reed switch 24 is closed by the magnetic flux of said magnet 30 passing through said reed switch 24 as indicated by the broken lines in FIG. 2, the transistor 21 is deenergized and the transistor 18 energized, whereby the slider 7 and the AC source line 2 are electrically shorted with each other. As a result, the SCR 3 is held deenergized thereafter, interrupting the current supply to the motor. Therefore, the motor stops rotating after rotating under mechanical inertia for only a very short period of time, upon closure of the reed switch 24.

If the reed switch 24 is opened again during the rotation under inertia of the motor, the SCR 3 will be reenergized and hence the motor will not stop rotating. For this reason, the dimension of the magnet 31 is so selected that the magnet will be held in opposed relation with the reed switch 24 through an ngle larger than the angle of rotation of the motor under inertia.

Therefore, when the switch 17 has been closed, the magnet 30 is brought into opposed relation with the reed switch 24 within one complete revolution of the operating shaft 32 and thus the needle is automatically stopped in its upper position.

The stoppage of the motor and the sewing machine results in interruption of current supply to the capacitor 27. Therefore, the current stored in the capacitor 27 is completely discharged in about 1 second and thus the bias source for the transistor 21 disappears. About I second after the sewing machine has automatically been stopped in the predetermined position, the motor and the sewing machine will not be placed in operation even if the operator inadvertently rotates the sewing machine to bring the magnet 30 out of opposed relation with the reed switch 24 and open said reed switch.

According to the present invention, as described above, the SCR 3 is promptly energized and the motor starts rotating upon opening of the switch 17, and the capacitor 27 is charged to provide a bias source for the transistor 21 upon opening of the switch 24. Therefore, by closing the switch 17 immediately after it has been opened, it is possible to rotate the sewing machine one revolution and automatically stop it in the original position. Namely, a stitch by stitch sewing operation can be attained easily and positively.

It will be obvious that if it is desired to automatically stop the needle always in its lower position, this can be attained by changing the relative position of the reed switch 24 and the magnet 30.

As will be understood from the embodiment described above, with the needle stop apparatus for a sewing machine according to the invention the current supply to the motor 5 is interrupted by electrically shorting the gate trigger signal generator 11 when the needle has been located in a predetermined position upon closure of a first switch (corresponding to the switch 17), whereby it is possible to stop the needle in a desired position. Furthermore, even if the needle is moved manually upon passage of a predetermined time after the needle has been stopped, the motor will not start running again, whereby the safety of the sewing machine is enhanced. Still further, with the apparatus of the invention, a stitch by stitch sewing operation can easily be attained and the sewing operation efficiency can be enhanced.

Referring now to FIGS. 4 to 6, there is shown another embodiment of the invention. In these FlGS., reference numerals 41, 42 designate AC source lines and between these AC source lines are connected in series an SCR 43 and the field winding 44 and the armature 45 of an associated series commutator motor. Also connected between the AC source lines 41 and 42 is a gate trigger signal generator 51 which consists ofa series circuit of a resistor 46, a variable resistor 48 having a slider 47, a resistor 49 and a diode S0. The diode 50 is connected in such a position that the cathode side thereof faces the AC source line 42. The slider 47 and the gate terminal 52 of the SCR 43 are connected with each other through a diode 53. The diode 53 is positioned with the cathode thereof facing the gate terminal 52.

A resistor 55 is connected between the gate terminal 52 and the cathode terminal 54 of the SCR 43 to protect the gate of said SCR. A,diode 56 is connected on the positive electrode side thereof to the junction of the resistors 48 and 49 of the gate trigger signal generator 51, and a switch 57 is connected at one terminal to the negative electrode side of said diode 56. A transistor 58 has its collector connected to the other terminal of the switch 57 and its emitter to the AC source line 42. The diode 56 is provided for the purpose of preventing inverse voltage breakage of the transistor 58 and is unnecessary when the resistance to inverse voltage of said transistor is large.

The operation of the switch 57 is associated with the vertical movement of the slider 47 of the variable resistor 48 in such a manner that said switch 57 is closed only when the slider 47 is at the lowest end of its stroke, and is opened when the slider 47 is moved upward slightly.

The base of the transistor 58 is connected to one terminal of the resistor 59 and the other terminal of said resistor 59 is connected to one terminal of a resistor 60 and the collector of a transistor 61. The other terminal of the resistor 60 is connected to the negative electrode of a diode 62, a capacitor 63 and a resistor 64. The positive electrode of the diode 62 is connected to the AC source line 41 and the other terminal of the capacitor 63 is connected to the AC source line 42 and further the other terminal of the resistor 64 is connected to the base of the transistor 61 and a changeover switch 65. The emitter of the transistor 61 is connected to the AC source line 42.

The changeover switch 65 has a first contact and a second contact which are connected to a reed switch 66 and a reed switch 67 respectively. The reed switches 66 and 67 are in turn connected to the AC source line 42 at their other terminals. These reed switches 66 and 67 are mounted on a stationary portion of the head 68 of the sewing machine in vertically symmetrical relation with respect to the operating shaft 69 of the machine as shown in FIG. 5.

On a flywheel 70 of the machine which is operatively connected with the needle, is mounted a magnet 71 at such a location that it is opposed by the reed switch 66 when the needle is in its upper position, and is opposed by the reed switch 67 when the needle is in its lower position. An electric motor is housed in the body of the sewing machine, with the drive shaft thereof operatively connected with the operating shaft 69 through a belt or gears.

FIG. 6 shows the relative position of the reed switches and the magnet as viewed in the direction of arrows Vl-Vl of FIG. 5, when the needle is in its upper position and the reed switch 66 is opposed by the magnet 70. The capacitor 63 is constantly charged through the diode 62 whenever the AC source lines 41 and 42 are impressed with voltage. Therefore, the capacitor 63 can be regarded as a sort of battery. If a bias voltage is not impressed on the transistor 61 when the slider 47 is at the lowest end of its stroke and the switch 57 is closed, a bias voltage is impressed across the base and emitter of the transistor 58 from the capacitor 63 through the resistors 60 and 59, to keep said transistor 58 energized. Therefore, the slider 47 and the AC source line 42 are electrically shorted through the transistor 58 and a trigger voltage is not impressed on the gate of the SCR 43. Consequently. the SCR 43 is held in the deenergized state and hence the motor is held inoperative. Now, when the slider 7 is slightly moved upward to open the switch 57 operatively associated therewith, the impedance between the slider 47 and the AC source line 42 is dissociated from the transistor 58. Therefore, when the AC source line 41 is charged with positive voltage, a current which varies in the form of a sine wave flows from the AC source line 41 to 42 through the resistor 46, the variable resistor 48, the resistor 49 and the diode 50. As a result, a voltage in proportion to the aforesaid current, that is, a voltage corresponding to the positive half wave of the AC source voltage, develops across the slider 47 and the AC source line 42. The SCR 43 is energized at the phase wherein the voltage reaches a value large enough to trigger the gate of said SCR, and thus the motor is set in operation. The voltage developed across the slider 47 and the AC source line 42 becomes larger as the slider 47 is moved upward and accordingly the angle of energization of the SCR 43 becomes larger and the speed of the motor increases.

On the other hand, when the AC source line 41 is charged with negative voltage, that is, the voltage corresponding to the negative half wave of the source voltage, a reverse voltage is impressed on the SCR 43, so that the SCR 43 blocks the current being supplied to the motor. However, the motor continues to rotate under mechanical inertia until the next positive halfcycle comes.

Now, when the slider 47 is moved downward to the lowest end of its stroke to stop the motor, the switch 57 is closed and the transistor 58 is again connected between the slider 47 and the AC source line 42. in this case, however, if the transistor 58 is in the energized state, the slider 47 and the AC source line 42 will be electrically shorted with each other and the SCR 43 will not be energized, whereas if the transistor 58 is in the deenergized state, no change will be caused by the transistor 58 between the slider 47 and the AC source line 42, and the SCR 43 will be energized at every half cycle, even after the switch 57 is closed, and the motor will continue to rotate at a predetermined low speed. Namely, whether the motor stops or not after the switch 57 has been closed is determined by whether the transistor 58 is in the energized state or in the deenergized state. Whether the transistor 58 is in the energized state or in the deenergized state is determined by whether the transistor 61 is in the deenergized state or in the energized state. The transistor 61 is deenergized when the reed switch 66, connected to the changeover switch 65, is closed, and is energized during the rest of the time.

As stated, the reed switch 66 is mounted on the stationary portion of the head 68 of the sewing machine and the magnet 71 is mounted on the flywheel 70 mounted on the operating shaft 32 of the machine for rotation therewith, as shown in FIG. 5. Therefore, when the needle is located in its upper position upon closure of the switch 57, and the reed switch 66 is opposed by the magnet 71 and closed by the magnetic flux of said magnet 71 passing through said reed switch as indicated by the broken lines in FIG. 5, the transistor 61 is deenergized and the transistor 58 is energized, whereby the slider 47 and the AC source line 42 are electrically shorted with each other. As a result, the SCR 43 is held deenergized thereafter, interrupting the current supply to the motor. Therefore, the motor stops running after rotating under mechanical inertia for only a very short period of time, upon closure of the reed switch 66. 1f the reed switch 66 is opened again during the rotation under the inertia of the motor, the SCR 43 will be reenergized and hence the motor will not stop rotating. For this reason, the dimension of the magnet 71 is so selected that the magnet will be held in opposed relation with the reed switch 66 through an angle larger than the angle of rotation of the motor under inertia. Therefore, when the switch 57 has been closed, the magnet 71 is brought into opposed relation with the reed switch 66 within one complete revolution of the operating shaft 69 and thus the needle is automatically stopped in its upper position. By closing the switch 57 immediately after it has been opened, it is possible to rotate the sewing machine one revolution and automatically stop it in the original position.

Where it is necessary to shift the needle to its lower position after it has been stopped in its upper position, the changeover switch 65 is switched over to the reed switch 67, whereby the bias voltage is again impressed on the transistor 61 and the needle is shifted to its lower position, as will readily understood from the foregoing description. It is of course possible to shift the needle from the lower position to the upper position by carrying out the foregoing operation in a reverse way.

With the needle stop apparatus of the type described above, the needle stop position can optionally be selected at either the upper position or the lower position, by switching the changeover switch 65. In addition, the needle can intermittently be shifted upwardly and downwardly, by switching the changeover switch 65 alternately in both directions, so that a stitch by-stitch sewing operation can simply be attined.

In FIG. 7, there is shown still another embodiment of the present invention. In this FlG., reference numerals 81, 82 designate AC source lines and between these AC source lines are connected in series an SCR 83 and the field winding 84 and the armature 85 of an associated series commutator motor which drives the needle of a sewing machine. Also connected between the AC source lines is a gate trigger signal generator 91 consisting of a series circuit of a resistor 86, a variable resistor 88 having a slider 87, a resistor 89 and a diode 90. The diode 90 is connected in such a position that the cathode side thereof faces the AC source line 82. The slider 87 and the gate terminal 92 of the SCR 83 are connected with each other through a diode 93. The diode 93 is connected in such a position that the cathode side thereof faces the gate terminal 92.

A resistor is connected between the gate terminal 92 and the cathode terminal 94 of the SCR 83 to protect the gate of said SCR. A diode 96 is connected on the positive electrode side thereof to the junction of the resistors 88 and 89 of the gate trigger signal generator 91, and a switch 97 is connected at one terminal to the negative electrode side of said diode 96. A transistor 98 has its collector connected to the other terminal of the switch 97 and its emitter to the AC source line 82. The diode 96 is provided for the purpose of inverse voltage breakage of the transistor 98 and is unnecessary when the resistance to inverse voltage of said transistor is large.

The operation of the switch 97 is associated with the vertical movement of the slider 87 of the variable resistor 88 in such a manner that said switch 97 is closed only when the slider 87 is at the lowest end ofits stroke, and is opened when the slider 87 is slightly moved upward therefrom.

The base of the transistor 98 is connected to the collector of a transistor 100 through a resistor 99. On the other hand, the collector of the transistor 100 is connected to one terminal of a DC power source means E, through a resistor 101. The other terminal of the DC power source means E, is connected to the AC source line 82.

The DC power source means E, constantly generates a voltage when the AC source lines 81 and 82 are charged, and the polarity of the voltage is negative at the terminal connected to the AC source line 82. The voltage generated by the DC power source means E, corresponds to the terminal voltage of the capacitor 23 of the apparatus of FIG. 1.

The emitter of the transistor 100 is connected to the AC source line 82 and the base thereof is connected to a DC power source means E through a resistor 102 and also directly to a switch means S (corresponding to the reed switch 24 of the apparatus of FIG. 1). The other terminals of the DC power source means E and the switch means S are connected to the AC source line 82 respectively.

The DC power source means E is so designed that it is charged immediately the SCR 83 is energized, and the current stored therein is completely discharged on passage of a predetermined time after the SCR 83 is deenergized. The voltage of the DC power source means E corresponds to the terminal voltage of the capacitor 27 of the apparatus shown in FIG. 1. The switch means S is so designed that it is turned on when the needle is in a predetermined position and is turned off when the needle is shifted from said predetermined position.

In addition to the transistor 98, the collector of a transistor 103, a resistor 104 and the negative electrode ofa diode 105 are also connected to one terminal of the switch 97. The emitter of the transistor 103 is connected to the AC source line 82 and the base thereof has the other terminal of the resistor 104, the other terminal of the diode 105 and a capacitor 106 connected thereto. The other terminal of the capacitor 106 is connected to the AC source line 82.

The circuit constructed as described above operates in the following manner: Namely, when the AC source lines 81, 82 are charged and the switch 97 is closed, a bias voltage is impressed on the transistor 98 from the DC power source means E, through the resistors 101 and 99, to keep said transistor in the energized state, and the slider 87 and the AC source line 82 are electrically shorted, so that the SCR 83 is held deenergized and the motor is held inoperative.

When the slider 87 is moved slightly upwardly to open the switch 97 operatively associated therewith, the electrical shorting of the slider 87 and the AC source line 82 is disrupted, so that a voltage corresponding to the positive half wave of the AC source voltage develops across the slider 87 and the AC source line 82 in the case when the AC source line 81 is charged with positive voltage. The SCR 83 is energized at the phase wherein the aforesaid voltage reaches a value large enough to trigger the gate of said SCR, and thus the motor is set in motion.

The angle of energization of the SCR 83 becomes larger and the speed of the motor increases as the slider 87 is moved upwardly, On the other hand, when the AC source line 81 is charged with negative voltage, i.e., the voltage corresponding to the negative half wave of the source voltage, the SCR 83 is impressed with an inverse voltage and the current supply to the motor is blocked by said SCR. However the motor continues to rotate under mechanical inertia until the next positive half cycle comes.

Now, when the slider 87 is moved to the lowest end of its stroke to stop the motor, the switch 97 is closed and the transistor 98 is again connected between the slider 87 and the AC source line 82. The switch means S is turned on when the needle has been located in the predetermined position after closure of the switch 97, whereby the DC power source means E is shorted and no bias voltage is impressed on the transistor 100, holding said transistor in the deenergized state.

In this case, the transistor 98 is energized by the bias voltage which is impressed thereon from the DC power source means E, through the resistors 101 and 99. Thus, the circuit of the needle stop apparatus is returned to the state before the motor is set in motion, and themotor stops running. After the power of the DC power source means E has exhausted upon stoppage of the motor, the motor is started again even when the position of the needle is shifted by manual operation and the switchmeans S is turned off.

Hereinabove, description has been given of the normal operation of the apparatus. Now, consider the case wherein the needle is located in a position other than the predetermined position immediately after the switch 97 has been closed to stop the operation, and the cloth being sewn is drawn into the sewing machine in that position of the needle, causing locking of the machine and the motor,

In this case, the DC power source means E is still in the charged state and the switch means S is in the OFF" position. Therefore, if the transistor is in the energized stage, the transistor 98 is held in the deenergized state and the interrelation between the slider 87 and the AC source line 82 is sub jected to no change by the closure of the switch 97. The gate trigger signal generator 91 generates a gate trigger signal at each cycle of the power source and hence the SCR 83 is energized at a predetermined angle at each cycle.

However, the current flows into the capacitor 106 through the resistor 104 since immediately after the switch 97 has been closed and said capacitor is charged with a predetermined time constant. When the current stored in the capacitor 106 has reached the cutoff voltage of the transistor 103, said transistor 103 is energized, electrically shorting the slider 87 and the AC source line 82 with each other.

Namely, the slider 87 and the AC source line 82 are electrically shorted in a predetermined period of time after the switch 97 is closed, even when the transistor 98 is not energized, and thus the SCR 83 is deenergized, interrupting the current supply to the motor. After passage of a predetermined time upon deenergization of the SCR 83, the power of the DC power source means E is exhausted, so that the transistor 98 is energized from that point independently of the state of the switch means S.

The diode 105 is a germanium diode, the forward stopping voltage of which is sufiiciently lower than the cutoff voltage of the transistor 103. When the transistor 98 is energized, the charge stored in the capacitor 106 is promptly discharged through the diode 105 and the transistor 98, and the entire circuit is returned to the state before the motor is started.

As may be understood from the foregoing description, in the needle stop apparatus of the invention described above the transistor 103, the resistor 104, the diode 105 and the capacitor 106 as a whole serve as a sort of timer, whereby when the motor and the sewing machine are in a locked condition upon closure of the switch-97, the current supply to the motor is interrupted after passage of a predetermined time, independently of the position of the needle, to protect the motor as well as to ensure the safety of the operator What is claimed is:

1. A needle stop apparatus for a sewing machine, comprising an electric motor for driving a needle, a solid state controlled rectifier element connected in series with said motor and thence to an AC power source, a gate trigger signal generator including a signal level adjusting variable resistor element, means for connecting the slider of said variable resistor element and the gate terminal of said solid state controlled rectifier element with each other, a switch operatively associated with the slider of said variable resistor element and adapted to be closed when said signal level is lowest, a variable impedance element connected in parallel with a portion of said gate trigger signal generator through said switch and means for changing the impedance of said variable impedance element upon detecting the position of said needle.

2. A needle stop apparatus for a sewing machine, comprising an electric motor for driving a needle, a solid state controlled rectifier element (3) connected in series with said motor and then to an AC power source (1,2), a gate trigger signal generator (11) including a signal level adjusting variable resistor element (8), means (13) for connecting the slider (7) of said variable resistor element (8) and the gate terminal (12) of said solid stage controlled rectifier element (3) with each other, a first switch (17) operatively associated with the slider (7) of said variable resistor element (8) and adapted to be closed when said signal level is lowest, a transistor (18) have the emitter and collector thereof connected in parallel to a portion of said gate trigger signal generator (11) through said first switch (17), a transistor (21) connected to the base of said transistor (18), a power source circuit (22,23) which is charged constantly during the period when said AC power source (1,2) is impressed and supplies a voltage to the base of said transistor (21), a second switch (24) connected to the base of said transistor (21) and adapted to be opened or closed upon detecting the position of the needle, and a power source circuit (28, 27, 25) for supplying a voltage to the base of said transistor (21), said power source circuit (28, 27, 25) being charged when said solid state controlled rectifier element (3) is energized and discharging the current stored therein when said solid state controlled rectifier element (3) is deenergized, and the voltage of said power source circuit being reduced to zero in a predetermined time,

3. A needle stop apparatus for a sewing machine, comprising an electric motor for driving a needle, a solid state controlled rectifier element (43) connected in series with said motor and then to an AC power source (41, 42), a gate trigger signal generator (51) including a signal level adjusting variable resistor element (48), means (53) for connecting the slider (47) of said variable resistor element (48) and the gate terminal (52) of said solid stage controlled rectifier element (43), a first switch (57) operatively associated with the slider (47) of said variable resistor element (48) and adapted to be closed when said signal level is lowest, a transistor (58) having the emitter and collector thereof connected in parallel to a portion of said gate trigger signal generator (51) through said first switch (57), a transistor (61) connected to the base of said transistor (58), a power source circuit (62, 63) which is constantly charged when said AC power source (41, 42) is impressed and supplies a voltage to the base of said transistor (61 and a plurality ofsecond switches (66, 67) connected to the base of said transistor (61) and adapted to be opened or closed upon detecting the position of the needle deviating from a preset position.

4. A needle stop apparatus for a sewing machine, comprising an electric motor for driving a needle, a solid state controlled rectifier element (83) for controlling the phase of an AC power source for said motor, said motor and said solid state controlled rectifier element being connected in series between the terminals (81, 82) of said AC power source, a gate trigger signal generator (91) for energizing said solid state controlled rectifier element (83), means (93) for connecting said gate trigger signal generator (91) to said solid state controlled rectifier element (83), a switch (97) connected between said gate trigger signal generator (91) and the terminal (82) of said AC power source and operatively associated with signal level adjusting means (87) for said gate trigger signalgenerator (91) so as to be closed when said signal level IS lowest, and safety means consisting of a transistor (103) having the emitter and collector thereof connected in series to said switch (97), a capacitor (106) connected between the base of said transistor 103) and the ter minal (82) of said AC power source, a resistor (104) connected between the base and the collector of said transistor (103) and a diode (105) connected in parallel to said resistor (104).

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1. A needle stop apparatus for a sewing machine, comprising an electric motor for driving a needle, a solid state controlled rectifier Element connected in series with said motor and thence to an AC power source, a gate trigger signal generator including a signal level adjusting variable resistor element, means for connecting the slider of said variable resistor element and the gate terminal of said solid state controlled rectifier element with each other, a switch operatively associated with the slider of said variable resistor element and adapted to be closed when said signal level is lowest, a variable impedance element connected in parallel with a portion of said gate trigger signal generator through said switch and means for changing the impedance of said variable impedance element upon detecting the position of said needle.
 2. A needle stop apparatus for a sewing machine, comprising an electric motor for driving a needle, a solid state controlled rectifier element (3) connected in series with said motor and then to an AC power source (1,2), a gate trigger signal generator (11) including a signal level adjusting variable resistor element (8), means (13) for connecting the slider (7) of said variable resistor element (8) and the gate terminal (12) of said solid stage controlled rectifier element (3) with each other, a first switch (17) operatively associated with the slider (7) of said variable resistor element (8) and adapted to be closed when said signal level is lowest, a transistor (18) have the emitter and collector thereof connected in parallel to a portion of said gate trigger signal generator (11) through said first switch (17), a transistor (21) connected to the base of said transistor (18), a power source circuit (22,23) which is charged constantly during the period when said AC power source (1,2) is impressed and supplies a voltage to the base of said transistor (21), a second switch (24) connected to the base of said transistor (21) and adapted to be opened or closed upon detecting the position of the needle, and a power source circuit (28, 27, 25) for supplying a voltage to the base of said transistor (21), said power source circuit (28, 27, 25) being charged when said solid state controlled rectifier element (3) is energized and discharging the current stored therein when said solid state controlled rectifier element (3) is deenergized, and the voltage of said power source circuit being reduced to zero in a predetermined time.
 3. A needle stop apparatus for a sewing machine, comprising an electric motor for driving a needle, a solid state controlled rectifier element (43) connected in series with said motor and then to an AC power source (41, 42), a gate trigger signal generator (51) including a signal level adjusting variable resistor element (48), means (53) for connecting the slider (47) of said variable resistor element (48) and the gate terminal (52) of said solid stage controlled rectifier element (43), a first switch (57) operatively associated with the slider (47) of said variable resistor element (48) and adapted to be closed when said signal level is lowest, a transistor (58) having the emitter and collector thereof connected in parallel to a portion of said gate trigger signal generator (51) through said first switch (57), a transistor (61) connected to the base of said transistor (58), a power source circuit (62, 63) which is constantly charged when said AC power source (41, 42) is impressed and supplies a voltage to the base of said transistor (61), and a plurality of second switches (66, 67) connected to the base of said transistor (61) and adapted to be opened or closed upon detecting the position of the needle deviating from a preset position.
 4. A needle stop apparatus for a sewing machine, comprising an electric motor for driving a needle, a solid state controlled rectifier element (83) for controlling the phase of an AC power source for said motor, said motor and said solid state controlled rectifier element being connected in series between the terminals (81, 82) of said AC power source, a gate trigger signal generator (91) for energizing said solid statE controlled rectifier element (83), means (93) for connecting said gate trigger signal generator (91) to said solid state controlled rectifier element (83), a switch (97) connected between said gate trigger signal generator (91) and the terminal (82) of said AC power source and operatively associated with signal level adjusting means (87) for said gate trigger signal generator (91) so as to be closed when said signal level is lowest, and safety means consisting of a transistor (103) having the emitter and collector thereof connected in series to said switch (97), a capacitor (106) connected between the base of said transistor (103) and the terminal (82) of said AC power source, a resistor (104) connected between the base and the collector of said transistor (103) and a diode (105) connected in parallel to said resistor (104). 